Removing and installing a heavy sash from a window is a two-person job, because the sash can weigh up to 90 pounds or more, as often occurs in schools, offices, and commercial and institutional buildings. The counterbalance systems for such heavy sashes provide correspondingly large forces. Locking the balance shoes in place to the window frames against the strong counterbalancing forces requires more strength and security than is offered by shoe locking systems intended for smaller residential window sashes.
When a smaller residential sash is removed from a window, it can be tilted from its vertical operating plane, and this transfers part of the sash weight from the support shoes to the person holding the sash. This is undesirable when the sash is especially heavy, because a person tilting a heavy sash might find he has encountered more weight than he can handle safely. Also, shoes that accommodate sash tilting are generally more complex than shoes for a sash that remains vertical.
Current solutions utilizing balance systems for removing and installing a heavy sash are described, for example, in U.S. Pat. No. 5,231,795, U.S. Pat. No. 6,892,494, and U.S. Pat. No. 6,948,279, the disclosures of which are hereby incorporated by reference herein in their entireties. Current balance systems for supporting and operating a heavy sash require large, multi-component structures that are expensive and complex to manufacture. Further, these systems are difficult to engage and disengage from window jambs as a whole and oftentimes from each individual component. In certain instances, when some of the components are engaged to one another, the components are not efficiently and securely attached. Significant play results between elements when engaged, which decreases the reliability and security of the balance system when installed and increases wear. For example, current balance systems engage a movable arm of a sash attachment to a carrier of a shoe counterbalance. Even when engaged, the arm of the sash attachment can move within a restricted area. Moreover, certain movements or jostling of the balance system, including the shoe or sash, may disengage certain components from one another.
Further, when the balance system and sash are installed, adjustment of the balance or spring component is not possible. The adjustment mechanism of the balance or spring component is obstructed by the large, multi-component balance system. Additionally, the size of the components limits the number of applications or jamb sizes into which the balance systems can fit. Current systems utilize, for example, large shoes with protruding carrier ledges to engage with pivoting arms mounted to the sashes. This configuration can only fit into jambs with sufficiently large sash-to-jamb spacing.
Accordingly, a balance system is needed that allows for a high-weight capacity balance with a low build-up rate. Locking the support shoes of the counterbalance system within the jambs should be secure and reliable, because of the large spring forces involved. Also, the sash support should make a heavy sash easy to raise and lower, and removal and replacement of the sash should be convenient and safe. Besides these requirements, an effective window system should reliably accomplish all the necessary balance functions, with elements that are inexpensive to manufacture and easy to install and maintain.